我有这样的linq查询:
var trfplanList = (from at in entities.tdp_ProviderAccomodationType
join ap in entities.tdp_ProviderAccomodationTariffPlan on at.PATID equals ap.FK_PATID
join ac in entities.tdp_ProviderAccomodationCategory on ap.FK_PACID equals ac.PACID
where at.FK_ProviderID == CityID && at.IsApproved == 0 && ap.IsApproved == 0 && ac.AccomodationCategory == "Double Occupy"
orderby at.AccomodationType,ap.FromDate,ap.SType
select new AccomodationTariff
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = Convert.ToDateTime(ap.FromDate),
ToDate = Convert.ToDateTime(ap.ToDate),
RoomTariff = Convert.ToDecimal(ap.Rate),
ExPAXRate = Convert.ToDecimal(at.PerPaxRate)
}).ToList();
我有两个问题:
在select new {}块中分配时,无法转换值吗?它在项目中给我一个错误。
我想从数据库中选择ExPAXRate
时使用'case',例如我以前编写的SQL:
CASE ap.SType WHAY'Off Season'THEN at.PerPaxRateOS ELSE at.PerPaxRate END as ExPAXRate
我可以在linq查询中使用这样的东西吗?
答案 0 :(得分:2)
在select new {}块
中分配时,无法转换值
不,你不能(遗憾地)。 EF不知道如何将其翻译成SQL。
我想使用'case'
您可以使用三元运算符(?
):
ExPAXRate = at.OffSeason ? at.PerPaxRateOS : at.PerPaxRate
(假设at.OffSeason
存在)。
转换问题的解决方案可能是首先投射到匿名类型,然后在内存中投射到AccomodationTariff
:
...
select new
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = ap.FromDate,
ToDate = ap.ToDate,
RoomTariff = ap.Rate,
ExPAXRate = at.PerPaxRate
}).AsEnumerable()
.Select(x => new AccomodationTariff
{
AccomodationType = x.AccomodationType,
SType = x.SType,
FromDate = Convert.ToDateTime(x.FromDate),
ToDate = Convert.ToDateTime(x.ToDate),
RoomTariff = Convert.ToDecimal(x.Rate),
ExPAXRate = Convert.ToDecimal(x.PerPaxRate)
}).ToList();